The present invention is in a process for manufacturing steel with a carbon content of less than 1 wt.-%, preferably less than 0.8 wt.-%, and most preferably less than 0.5 wt.-%, by reducing iron ore and refining the hot metal. Further, the invention also relates to an apparatus useful for practicing the process.
Iron with a carbon content of about 1 wt.-% is produced in a molten state and is referred to as steel. Today, steel is manufactured from raw or pig iron, sponge iron and scrap iron. In the manufacture of steel, the starting material, such as liquid pig iron is converted into steel by means of refining wherein the carbon contained in the liquid pig iron is oxidized by oxygen. At the same time, elements such as silicon, manganese, and phosphorous are at least partially removed from the liquid iron in an oxidized state which is contained in a slag. Subsequent to the refining, the steel can be further treated, if necessary, and withdrawn in a continuous or discontinuous manner. Whereas liquid pig iron is produced in a blast furnace, sponge iron is produced by solid state direct reduction of iron ore.
It is necessary to modify known manufacturing processes such that the efficiency of energy, iron ore and coal utilization is increased. Further, the use of scrap material should also be possible, and the generation of environmentally harmful waste products should be decreased.
EP-OS 237 811 discloses a process which permits the prereduction of iron ore even when low-grade coal is used. The process of EP-OS 237 811 accomplishes this object by providing for a two-stage melting reduction of iron ore, using fuel and an oxidizing gas. Iron ore is prereduced in a melting cyclone to essentially wuestite. In a subsequent iron bath reactor, liquid pig iron is produced.
The disclosure of U.S. Pat. No. 4,540,432 states as an object to provide a process for the continuous melting of sponge iron having a large particle size range, using solid carbonaceous fuel. The patent describes a process for this purpose, wherein melting of the sponge iron is carried out in an elongated, approximately horizontal reactor. In that process, sponge iron is charged into the center area of the reactor, carbonaceous fuel and oxygen-containing gases are blown into the melt and liquid slag and iron are withdrawn on opposite sides of the reactor. In order to economically melt sponge iron with a large particle size range using solid fuel, the sponge iron is charged into the center area comprising 20 to 40% of the total length of the reactor.
It is the object of the present invention to provide a process for the manufacture of steel which permits reduction of iron ore and the refining of the pig iron so produced to steel in a single reactor. The efficiency of energy use is optimized in this process with iron ore being used as a raw material.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects obtained by its use, reference should be had to the accompanying drawing and descriptive matter in which there is illustrated and described a preferred embodiment of the invention .